Rat Study Links SSRI Antidepressants to Signs of Autism

A new study has found that rats exposed at a young age to selective serotonin reuptake inhibitor (SSRI) antidepressants exhibit traits consistent with autism spectrum disorder (ASD). The study, conducted by researchers at the University of Mississippi Medical Center (UMCC) and the University of California, San Francisco (USCF), indicates that use of SSRI antidepressants during pregnancy might be one factor contributing to a dramatic rise in autism and ASD in children.

SSRI antidepressants include drugs like Prozac, Luvox, Paxil, Celexa and Zoloft. The incidence of pregnant women taking SSRIs has grown from about .5 percent in 1985 when the first one came on the market to nearly 10 percent today. At the same time, autism has also become more prevalent. In 1996, the rate of incidence was less than 1 in 1,000 births and by 2007 it reached about 1 in 200. The rates of incidence of ASD have roughly doubled every three-to-five years to 1 in 91 currently.

“The diagnosis has widened with the awareness that it’s a spectrum disorder that encompasses a whole range of communication problems, but that doesn’t account for all the increase by any means,” Dr. Ian Paul, UMMC professor of psychiatry and human behavior, said in a press release detailing the new study’s findings.

The rats in this study were administered Celexa (citalopram). Because rats are born at an earlier stage of brain development compared to humans (equivalent to the end of the sixth month of fetal development in humans), the animals in the study were given the drug after birth, during key stages of brain development.

According the press release, the investigators found the Celexa- treated animals were uninterested in play when young and displayed poor social behaviors as adults. The treated rats also showed abnormal responses to changes in their environment. For example, they froze at the sound of a novel tone and showed little interest in exploring new toys. The study authors pointed out that similar traits are often seen in human with ASD.

What’s more, autism-like behaviors occurred more often in the treated male rats than in treated females. Similarly, ASD is diagnosed more often in males.

The study in rats follows an epidemiologic study in humans, published in July in the Archives of General Psychiatry, which found that children of mothers who took SSRIs during the year prior to giving birth ran twice the normal risk of developing autism.

“While one must always be cautious extrapolating from medication effects in rats to medication effects in people, these new results suggest an opportunity to study the mechanisms by which antidepressants influence brain and behavioral development,” said Dr. Thomas R. Insel, director of the National Institute of Mental Health. “These studies will help to balance the mental health needs of pregnant mothers with possible increased risk to their offspring.”

The study authors did stress that their findings did not constitute proof that SSRI antidepressants cause autism. They urged expectant mothers or women seeking to become pregnant to speak with their doctors before ending treatment with an SSRI.

“A pregnant mother may do more harm to her baby through untreated depression than by taking prescribed SSRIs. This study is a starting point and a lot more research needs to be done.” said Dr. Rick C.S. Lin, professor of neurobiology and anatomical sciences at UMMC.